On macOS, there is a noninteractive bar (that I’ve only seen used as a tab bar) that appears at the top of the gameplay. Even if I go into Fullscreen mode, the bar is still there. I don’t know when it began appearing but it has just now made me want to make this post. All I have to do to make it appear is open any game and it appears 100% of the time.
I am on macOS Catalina but I have seen it happen on Sierra, High Sierra, and Mojave and on a different computer.
MacBook Pro (Retina, 13-inch, Mid 2014) and this issue also happens on another iMac we have. (I don’t know what the mac is but it’s running Mojave and it isn’t that new.)